Lift-balancing device

ABSTRACT

A static force balancing system attached to a lifting body flying on a free-flight suspension system in a wind tunnel which balances the static lift forces generated in excess of lifting body weight while permitting freedom of movement of the lifting body in response to dynamic forces. The static lift forces are balanced by the flow of pressurized air against a piston sliding loosely in a casing. Friction between piston and casing is essentially eliminated by a portion of the pressurized air leaking past the piston. Force variation with piston position is essentially eliminated by providing a pressure reservoir connected to the casing which acts as an accumulator.

United States Patent v 15] 3,695,101 Hanson Oct. 3, 1972 LIFT-BALANCINGDEVICE 2,331,304 10/1943 Carmody ..73/147 72 l P W. nvmor eny HansonHampton Va Primary Examiner-S. Clement Swisher [73] Assigneez The UnitedStates of America as Attorney-Howard J. Osborn and John R. Manningrepresented by the Administrator of the National Aeronautics and Space57 ABSTRACT Admmlstmuon A static force balancing system attached to alifting [22] Filed: Sept. 8, 1970 body flying on a free-flightsuspension system in a wind tunnel which balances the static lift forces[21] Appl' 70032 generated in excess of lifting body weight whilepermitting freedom of movement of the lifting body in [52] US. Cl...73/147 response to y forces- T Static lift forces are 51 Int. Cl...G0lm 9/00 balanced by the flow of pressurized air against a piston 58Field of Search ..73/147, 148 sliding loosely in a casing- Frictionbetween Piston and casing is essentially eliminated by a portion of the[56] References Cited pressurized air leaking past the piston. Forcevariation with piston position is essentially eliminated by providUNITED STATES PATENTS ing a pressure reservoir connected to the casingwhich ts l t 3,240,059 3/1966 Kiel .7 ..73/147 ac as accum a 3,276,25110/1966 Reed ..73/147 11 Claims, 1 Drawing Figure l5 l0 u RELATIVE WINDI? w IS TO ATMOSPHERE PAIENTEBncrs I972 3,695,101

TO ATMOSPHERE INVENTOR PERRY W. HANSON ATTORNEY LIFT-BALANCING DEVICEORIGIN OF THE INVENTION BACKGROUND OF THE INVENTION This inventionrelates to a force balancing device and more particularly to a supportsystem which balances static lift forces produced by a lifting bodyflying in a wind tunnel in excess of lifting body weight permitting freeresponse to dynamic forces acting on the lifting body. Dynamic stabilityand aeroelastic response testing of spacecraft and aircraft is presentlyperformed in wind tunnels with flying models having a free-flightsuspension system as described in US. Pat. No. 3,276,251. Thefree-flight suspension system described in the above patent is designedfor lg level flight conditions. Therefore, testing can be accomplishedonly when the model is producing lift equal to its own weight. Inmaneuvering, however, aircraft or spacecraft may produce high lift,greater than the weight of the aircraft or spacecraft. In order toconduct tests of wind tunnel models flying at high g maneuvering flightconditions on a free-flight suspension system, it was necessary todesign a static force balancing system which would balance out the liftproduced in excess of model weight. In order to obtain meaningful data,restraints placed on the model by the force balancing system in excessof the lift balanced must necessarily be minimal. That is to say thatstatic lift forces in excess of model weight must be balanced by theforce balancing system without influencing model response to dynamicforces.

SUMMARY OF INVENTION The static lift balancing system consists of apiston sliding loosely within a casing and connected to the lifting bodyby a linkage. The linkage consists of a rigid rod extending from thepiston to a point exterior to the casing and a flexible cable extendingfrom the rigid rod to the point of attachment on the model. Controlled,pressurized air is directed into the casing and against the pistoncreating a force which balances static lift in excess of model weight. Aportion of the pressurized air is permitted to leak past the sides ofthe piston essentially eliminating friction between the piston and thecasing wall. The pressurized air flows into the casing through apressure reservoir which serves as an accumulator. Since the volume ofthe pressure reservoir is large in comparison to the volume of thecasing, the pressure reservoir absorbs pressure changes, and thereforeforce changes, which are caused by movement of the piston within thecasing. Valves are provided to control the flow of pressured air intothe reservoir and to allow the escape of excess air from the pressurereservoir. Both the air that leaks past the piston and the excess airescaping from the pressure reservoir are exhausted into the atmospherethrough an exhaust buffer tank.

Accordingly, it is an object of the invention to provide a static forcebalancing system for a lifting body flying in a wind tunnel test sectionand subject to dynamic and static lift forces acting through the centerof gravity of the lifting body. The device will balance static forceswithout damping dynamic forces. The invention will support the flyingmodel near the center of the wind tunnel test section and will permitThe lifting body to oscillate in response to dynamic forces.

BRIEF DESCRIPTION OF THE DRAWING A more complete appreciation of theinvention and many of the attendant advantages thereof will be readilyapparent as the same becomes better understood by reference to thefollowing detailed description when considered in connection with theaccompanying drawing wherein:

The FIGURE is a schematic view of the novel liftbalancing device.

DESCRIPTION OF THE PREFERRED EMBODIMENT Referring now to the FIGURE,there is shown a wind tunnel test section 11 employing a relative wind10 for the testing of body lifting body 13. Body 13 is supported by thenormal free-flight cable support system 15 which is fully described inthe US. Pat. No. 3,276,251 and by a lift-balancing cable 17.Lift-balancing cable 17 is connected to a piston 19 which is housed in acasing 20. Pressurized air from a source of pressured air 21 passesthrough an inlet valve 23 into a pressure reservoir 25. Pressure inpressure reservoir 25 is maintained at the desired level by theconcerted operation of inlet valve 23 and exhaust valve 27. Air from thereservoir passes through pressure inlet valve 29 into easing 20 where itexerts a pressure force against piston 19. Some of this pressurized airis permitted to leak past piston 19 through a clearance 30 between thepiston and the casing wall. Clearance 30 is formed by the loose fit ofpiston 19 within casing 20. Air leaking past piston 19 enters exhaustbuffer tank 33 through line 31 and is exhausted into the atmosphere,together with the air passing through exhaust valve 27, through line 35.

OPERATION The operation of the present invention is now believedapparent. Lifting body 13 will fly in wind tunnel test section 11restrained only by a freedlight suspension system 15 provided that thelift produced equals the weight of the body 13. When it is desired totest body 13 in a higher lift configuration simulating maneuveringflight, the novel lift balancing support system must be used. A flexiblelift balancing cable 17 is attached to the body near its center ofgravity and to a piston 19 in the casing 20. As lift increases on body13, inlet valve 23 is opened allowing pressurized air from source 21 topass into casing 20 through pressure reservoir 25 and pressure inletline 29. Inlet valve 23 is manipulated to control the pressure actingagainst piston 19 so as to balance the lift produced by lifting body 13in excess of the weight of the lifting body.

Lifting body 13 may be raised or lowered in the tunnel test section 11through the opening and closing of inlet valve 23 or exhaust valve 27.Opening inlet valve 23 alone when body 13 is in stable flight willresult in a descent of body 13 toward the floor of wind tunnel testsection 1 l as the force acting on the piston 19 becomes greater thenthe excess lift force. Opening valve 27 alone with body 13 in stableflight will cause body 13 to rise toward the top of the wind tunnel testsection 1 1 as the excess lift force exceeds the force acting on piston19. With inlet valve 23 and exhaust valve 27 in the open or partiallyopen position, closing either valve alone will effect a resultantlifting body displacement (up or down) which is directly opposite tothat caused by opening the valve.

During normal testing, inlet valve 23 and exhaust valve 27 aremanipulated as pressure regulators to keep lifting body 13 in the centerof the wind tunnel test section 1 1. A portion of the pressurized airentering casing 20 leaks past piston 19 through clearance 30 betweenpiston 19 and the walls of casing 20 and essentially eliminates frictionbetween piston 19 and casing 20. Since the volume of pressure reservoir25 is large in comparison to that of casing 20, pressure changes causedby movement of piston 19 within casing 20 are essentially absorbed bypressure reservoir 25 which acts as an accumulator allowing piston 19 tomove within casing20 with negligible change in force due to body motion.Thus piston 19 is free to oscillate in casing 20 in response to randomexternal forces and body structural vibrations and dynamic stabilityphenomena, such as dutch roll, can affect the body with minimum dynamicrestraint from the lift-balancing support system. Pressurized airpassing through exhaust valve 27 or leaking around piston 19 entersexhaust buffer tank 33 and is exhausted into the atmosphere through line35. It is thus seen that the present invention balances the liftproduced by a lifting body flying in a wind tunnel in excess of liftingbody weight while leaving the body free to move in response to dynamicforces.

Although the invention has been described and illustrated in detail on aspecific embodiment thereof, it is to be understood that thisdescription is by Way of illustration only and is not to be taken aslimiting upon applicants invention. Obviously, there are manymodifications and variations of the present invention possible in thelight of the above teachings. Several tanks may be used as pressurereservoirs and any pressurized gas may be used in lieu of pressurizedair. Casing 20 may be designed with stops limiting the travel of piston19 to prevent lifting body 13 from exceeding prescribed limits ofmotion. Materials used in construction are those normally used forpressure vessels and lines.

What is claimed as new and desired to be secured by Letters Patent ofthe United States is:

1. A force balancing device comprising: a movable member acted upon byboth static and dynamic forces; a static force balancing system for saidmovable member including a casing member, means for transmitting a forcehoused within said casing member, linkage means connecting said movablemember with said means for transmitting a force, a source of pressurizedgas, means for controlling the flow of said pressurized gas against saidmeans for transmitting a force, means permitting a portion of thepressurized gas to leak past said means for transmitting a force andaccumulator means connected to said casing member, said accumulatormeans absorbing pressure changes in said casing member caused bymovement of said means of transmitting a force, said movement beingcaused by dynamic forces acting upon said movable member, whereby theflow of pressurized gas against and past said means for transmitting aforce balances said static forces and holds said movable member in anequilibrium position as to said static forces while allowing saidmovable body to move freely in response to said dynamic forces.

2. The device of claim 1 wherein the means permitting a portion of saidpressurized gas to leak past said means for transmitting a force is thedesign of said means for transmitting a force, said means fortransmitting a force having a cross-section smaller than that of saidcasing member providing a clearance between said casing member and saidmeans for transmitting a force, whereby the leakage portion of saidpressurized gas escapes through said clearance and essentiallyeliminates friction between said casing member and said means fortransmitting a force.

3. The device of claim 1 wherein said accumulator means consists of atleast one pressure reservoir having a volume which is large incomparison to the volume of said casing member.

4. The device of claim 1 wherein the movable member is a lifting bodyflying in a wind tunnel restrained by a free-flight suspension systemand by said static force balancing system.

5. The device of claim 1 wherein the movable member is a lifting modelflying in a wind tunnel, restrained by a free-flight suspension systemand by said static force balancing system, said means for transmitting aforce is a piston sliding loosely within said casing member, said meanspermitting a portion of the fluid to leak past said piston is aclearance between said piston and said casing member, said linkage meansis a rigid rod extending from said piston to a point exterior saidcasing member and a flexible cable extending from said push rod to saidlifting model, and said accumulator means includes at least one pressurereservoir connected to said casing member and having a volume large incomparison with said casing member for absorbing pressure changes insaid casing member caused by piston movement in response to dynamicforces acting on the lifting mode.

6. The device of claim 1 wherein said means for controlling the flowincludes inlet means connecting said source of pressurized gas with saidaccumulator means, said inlet means for admitting a controlled amount ofsaid pressurized gas into said accumulator means and exhaust meansattached to said accumulator means, said exhaust means for releasingcontrolled amounts of said pressurized gas from said accumulator means,whereby said inlet means and said exhaust means operate in concert tocontrol the flow of gas against the means for transmitting a force.

7. The device of claim 1 wherein the linkage means includes a rigidmember extending from the means for transmitting a force to a pointexterior to said casing and a flexible member extending from the rigidmember to the movable member.

8. A force balancing device comprising:

a movable member mounted for maneuvering in an air stream acted upon byboth static and dynamic forces;

a static force balancing system for said movable member including acasing member, means for transmitting a force housed within said casingmember, linkage means for connecting said movable member with said meansfor transmitting a force, said linkage means including a rigid memberextending from the means for transmitting a force to a point exteriorsaid casing member and a flexible member extending from the rigid memberto the movable member, a source of pressurized gas, means forcontrolling the flow of said pressurized gas against said means fortransmitting a force, and means permitting a portion of the pressurizedgas to leak past said means for transmitting a force, whereby the flowof pressurized gas against and past said means for transmitting a forcebalances said static forces and holds said movable member in anequilibrium position as to said static forces while allowing saidmovable body to move freely in response to said dynamic force.

9. The device of claim 8 wherein the rigid member is a rod and theflexible member is a cable.

10. A method for balancing static forces acting on a movable body whileleaving the movable body free to move in response to dynamic forcescomprising the steps of:

a. providing a movable body mounted for maneuvering in an air streambeing acted upon by static and dynamic forces;

connecting said movable body by a flexible linkage to a forcetransmitting means contained in a casing member;

c. controllably directing pressurized gas from a source of said gasagainst said force transmitting means creating a force which balancessaid static forces acting upon said movable member;

. permitting a portion of said pressurized gas to leak past said forcetransmitting means; (e) controlling the amount of gas that leaks pastsaid force transmitting means; whereby the static forces acting on amovable body are balanced while leaving the movable body free to respondto dynamic forces.

11. The method of claim 10 including the step of accumulatingpressurized gas from said source of pressurized gas and from said casingmember to absorb pressure changes in said casing member caused bymovement of said force transmitting means and wherein the step ofpermitting includes providing a clearance between said forcetransmitting means and said casing member for the leakage of saidpressurized gas.

1. A force balancing device comprising: a movable member acted upon byboth static and dynamic forces; a static force balancing system for saidmovable member including a casing member, means for transmitting a forcehoused within said casing member, linkage means connecting said movablemember with said means for transmitting a force, a source of pressurizedgas, means for controlling the flow of said pressurized gas against saidmeans for transmitting a force, means permitting a portion of thepressurized gas to leak past said means for transmitting a force andaccumulator means connected to said casing member, said accumulatormeans absorbing pressure changes in said casing member caused bymovement of said means of transmitting a force, said movement beingcaused by dynamic forces acting upon said movable member, whereby theflow of pressurized gas against and past said means for transmitting aforce balances said static forces and holds said movable member in anequilibrium position as to said static forces while allowing saidmovable body to move freely in response to said dynamic forces.
 2. Thedevice of claim 1 wherein the means permitting a portion of saidpressurized gas to leak past said means for transmitting a force is thedesign of said means for transmitting a force, said means fortransmitting a force having a cross-section smaller than that of saidcasing member providing a clearance between said casing member and saidmeans for transmitting a force, whereby the leakage portion of saidpressurized gas escapes through said clearance and essentiallyeliminates friction between said casing member and said means fortransmitting a force.
 3. The device of claim 1 wherein said accumulatormeans consists of at least one pressure reservoir having a volume whichis large in comparison to the volume of said casing member.
 4. Thedevice of claim 1 wherein the movable member is a lifting body flying ina wind tunnel restrained by a free-flight suspension system and by saidstatic force balancing system.
 5. The device of claim 1 wherein themovable member is a lifting model flying in a wind tunnel, restrained bya free-flight suspension system and by said static force balancingsystem, said means for transmitting a force is a piston sliding looselywithin said casing member, said means permitting a portion of the fluidto leak past said piston is a clearance between said piston and saidcasing member, said linkage means is a rigid rod extending from saidpiston to a point exterior said casing member and a flexible cableextending from said push rod to said lifting model, and said accumulatormeans includes at least one pressure reservoir connected to said casingmember and having a volume large in comparison with said casing memberfor absorbing pressure changes in said casing member caused by pistonmovement in response to dynamic forces acting on the lifting mode. 6.The device of claim 1 wherein said means for controlling the flowincludes inlet means connecting said source of pressurized gas with saidaccumulator means, said inlet means for admitting a controlled amount ofsaid pressurized gas into said accumulator means and exhaust meansattached to said accumulator means, said exhaust means for releasingcontrolled amounts of said pressurized gas from said accumulator means,whereby said inlet means and said exhaust means operate in concert tocontrol the flow of gas against the means for transmitting a force. 7.The device of claim 1 wherein the linkage means includes a rigid memberextending from the means for transmitting a force to a point exterior tosaid casing and a flexible member extending from the rigid member to themovable member.
 8. A force balancing device comprising: a movable membermounted for maneuvering in an air stream acted upon by both static anddynamic forces; a static force balancing system for said movable memberincluding a casing member, means for transmitting a force housed withinsaid casing member, linkage means for connecting said movable memberwith said means for transmitting a force, said linkage means including arigid member extending from the means for transmitting a force to apoint exterior said casing member and a flexible member extending fromthe rigid member to the movable member, a source of pressurized gas,means for controlling the flow of said pressurized gas against saidmeans for transmitting a force, and means permitting a portion of thepressurized gas to leak past said means for transmitting a force,whereby the flow of pressurized gas against and past said means fortransmitting a force balances said static forces and holds said movablemember in an equilibrium position as to said static forces whileallowing said movable body to move freely in response to said dynamicforce.
 9. The device of claim 8 wherein the rigid member is a rod andthe flexible member is a cable.
 10. A method for balancing static forcesacting on a movable body while leaving the movable body free to move inresponse to dynamic forces comprising the steps of: a. providing amovable body mounted for maneuvering in an air stream being acted uponby static and dynamic forces; b. connecting said movable body by aflexible linkage to a force transmitting means contained in a casingmember; c. controllably directing pressurized gas from a source of saidgas against said force transmitting means creating a force whichbalances said static forces acting upon said movable member; d.permitting a portion of said pressurized gas to leak past said forcetransmitting means; (e) controlling the amount of gas that leaks pastsaid force transmitting means; whereby the static forces acting on amovable body are balanced while leaving the movable body free to respondto dynamic forces.
 11. The method of claim 10 incLuding the step ofaccumulating pressurized gas from said source of pressurized gas andfrom said casing member to absorb pressure changes in said casing membercaused by movement of said force transmitting means and wherein the stepof permitting includes providing a clearance between said forcetransmitting means and said casing member for the leakage of saidpressurized gas.